1. Field of the Invention
The present invention relates to a droplet discharge head and inkjet recording apparatus, and more specifically to the structure for a droplet discharge head effective for removing bubbles within a pressure chamber in communication with a nozzle (droplet discharge port), and to an inkjet recording apparatus that uses the head.
2. Description of the Related Art
Inkjet recording apparatuses deposit ink droplets on a recording medium by relatively moving recording paper or another recording medium with respect to a recording head provided with ink discharge nozzles while discharging ink from the recording head in accordance with a print signal, and an image is formed on the printing medium by the ink dots.
Inkjet heads (recording heads) are configured to feed ink to a pressure chamber in communication with a nozzle, to impart pressure variation to the liquid inside the pressure chamber, and to discharge droplets from the nozzle, so when bubbles are present inside the pressure chamber, the required pressure for discharge is not transmitted to the ink and a discharge defect is created. To prevent such a discharge defect, an action (suctioning action) is carried out to suction away the ink mixed with bubbles inside the pressure chamber and to eliminate the ink together with the bubbles. However, this action has a drawback in that ink consumption for carrying out the suctioning action is increased.
To address this problem, the inkjet head disclosed in Japanese Patent Application Publication No. 6-24000 is configured such that two ink supply ports with different flow resistances are provided to an ink chamber in communication with a nozzle. These two ink supply ports are each connected to a separate reserve tank, and bubbles inside the ink chamber can be drawn into one of the reserve tanks by a pump that controls the switching of ink circulation modes (ink circulation direction).
Also, a structure is disclosed in Japanese Patent Application Publication No. 2002-355961 whereby a circulation flow channel is provided to a common flow channel that is in communication with a plurality of pressure chambers, and bubbles in the common flow channel are recovered together with ink.
Additionally, a structure is disclosed in Japanese Patent Application Publication No. 2002-254643 whereby ink that is to be fed to a nozzle is circulated in a thermal jet-type inkjet head provided with a heating resistor for generating the heat energy required for ink discharge.
However, the configurations proposed in Japanese Patent Application Publication Nos. 6-24000 and 2002-254643 result in the release of pressure to the circulation channel during discharge driving, so a greater amount of discharge actuator power is required. The configuration proposed in Japanese Patent Application Publication No. 2002-355961 allows bubbles inside the common flow channel to be removed, but bubbles inside the pressure chamber cannot be removed.